A vehicle is equipped with a transmission system including an automatic transmission to convert driving force from an engine according to a driving state, and a transfer mechanism to distribute the driving force.
There are some automatic transmissions in which a normal gear-type manual transmission is automated so as to increase transfer efficiency of driving force as compared to the normal gear-type manual transmission. Some automatic transmissions, in which the normal gear-type manual transmission is automated, include an input shaft in connection with an engine through a main clutch, an output shaft in connection with drive wheels, a plurality of gear trains to transmit the driving force from the input shaft to the output shaft at different ratios, and a gear-shifting mechanism to change the engagement of the gear trains, with the shifting mechanism being operated when gears shift.
Such automatic transmissions based on the manual transmission are disclosed in JP Laid-Open No. 2001-227600 Official Gazette and JP Laid-Open No. 2000-97297 Official Gazette. In the automatic transmission based on the manual transmission according to JP Laid-Open No. 2001-227600, a third-speed drive gear is employed as an input-side gear train of a sub-clutch, and a fifth-speed drive gear is also employed as an output-side gear train so as to commonly and effectively utilize parts and manufacture equipment. An automatic transmission based on the manual transmission according to JP Laid-Open No. 2000-97297 comprises a dual input shaft having a first input shaft and a second input shaft concentric with the first shaft, and a dual clutch having two clutches for transmitting engine torque to the input shaft. Layout of dual input shaft and dual clutch is well arranged.
In the conventional automatic transmission in which the gear-type manual transmission is automated, a so-called “snow mode” is provided to control the drive wheel's spin to allow the vehicle to start easily on a slippery road, such as a snowy or icy road.
According to the automatic transmission with the snow mode, the snow mode controls the driving force at motion start-up of the vehicle, in most cases, not in the first (i.e. low) speed position but in the second-speed position so as to prevent the drive wheels from spinning on the slippery road. The normal snow mode is changed by a mode change switch in an auto-shift mode. However, the driver may forget to return the mode change switch, which remains in the snow mode, so that the vehicle always starts in the second-speed position. This results in a large load on devices during motion start-up, such as a torque converter and a start clutch, and can be a cause of fault or failure.
In addition, in the manual shifting for the automatic transmission based on the manual transmission, the second-speed position is selected for motion start-up on the slippery road. However, the manual shift must always be selected after the vehicle is started, which is troublesome.
Further, at start-up of the vehicle, the vehicle may move forward or backward. There is only one gear ratio for moving backward, so that a snow mode for backward motion generally is not provided, which results in difficulty in vehicle motion start-up on a slippery road.
Still further, when spinning of the drive wheel is detected on the slippery road, control of an accelerator degree by an electric throttle is required to control the driving force. However, response of the control is not good, so that appropriate control is difficult.
In addition, a throttle valve can be operated electronically to adjust the throttle opening degree for controlling a torque reduction. However, the driving force at motion start-up of the vehicle is determined by a start clutch and, in relation to the torque reduction control, the response of the control may not be good. Further, the throttle valve can also be operated by the accelerator pedal by the driver, but the engine does not respond to the throttle opening degree by the accelerator pedal, which results in the driver's uncomfortable feeling.